PROTOCOL OUTLINE: Patients undergo a glucose tolerance test over 3 hours and a potassium body scan on day 1. Patients undergo an indirect calorimetry over 20 minutes on day 2. Patients receive stable-labeled leucine and stable-labeled glucose IV over 3 hours followed by insulin and glucose IV over 4-4.5 hours on day 2 using the hyperinsulinemic euglycemic clamp technique.